Conventionally, with respect to parts for industrial machines, transporting machines and the like such as, for example, a power shovel, a bulldozer, a hopper, a bucket or a dump truck used in a construction site, a civil engineering site, a mine or the like, wear is generated due to a contact of the part with earth, sand or the like. Accordingly, in manufacturing the above-mentioned parts, a steel material having excellent abrasion resistance is used for extending lifetime of the parts. In an actual in-use environment, various states such as a dry state or a wet state are considered as a state of earth, sand or the like. Particularly, there may be a case where earth, sand or the like in a wet state contain a corrosive material. Accordingly, the wear due to earth, sand or the like in a wet state becomes wear in an environment which contains the corrosive material, that is, so-called corrosive wear. This corrosive wear has been known as an extremely severe wear environment. In view of the above, there has been a demand for an abrasion resistant steel material having excellent corrosive wear resistance.
The use of these industrial machines, transporting machines and the like in a low-temperature range of 0° C. or below is also considered. Accordingly, a steel material which is used for parts of these industrial machines, transporting machines and the like is requested to possess the excellent low-temperature toughness in addition to the abrasion resistance and corrosive wear resistance.
To satisfy such a request, for example, patent literature 1 proposes a method of manufacturing a high-hardness abrasion resistant steel having excellent low-temperature toughness, wherein hot rolling is applied to a steel slab having the composition containing by mass %: 0.30% to 0.50% C, proper amounts of Si, Mn, Al, N, Ti, Nb and B respectively, and 0.10% to 0.50% Cr and 0.05% to 1.00% Mo, thereafter, quenching treatment is applied to the hot rolled steel plate from a temperature of Ar3 transformation point or above and, subsequently, the quenched plate is tempered thus obtaining high-strength abrasion resistant steel. According to the description of the technique described in patent literature 1, the improvement of hardenability and the improvement of low-temperature toughness through strengthening of grain boundaries are achieved by allowing the steel to contain a large amount of Cr and a large amount of Mo. Further, according to the description of the technique described in patent literature 1, the further enhancement of low-temperature toughness is achieved by applying tempering treatment to the steel.
Patent literature 2 proposes a high toughness abrasion resistant steel plate which has the composition containing by mass %: 0.18% to 0.25% C, 0.10% to 0.30% Si, 0.03% to 0.10% Mn, proper amounts of Nb, Al, N and B respectively, 1.00% to 2.00% Cr, and more than 0.50% to 0.80% Mo, and exhibits excellent toughness and excellent delayed fracture resistance after water quenching and tempering. According to the description of a technique described in patent literature 2, by suppressing the content of Mn to a low level, and by allowing the steel plate to contain a large amount of Cr and a large amount of Mo, hardenability can be enhanced so that predetermined hardness can be ensured and, at the same time, toughness and delayed fracture resistance can be enhanced. Further, according to the description of the technique described in patent literature 2 further improves low-temperature toughness by further applying tempering.
Patent literature 3 proposes a high toughness and abrasion resistant steel which has the composition containing by mass %: 0.30% to 0.45% C, 0.10% to 0.50% Si, 0.30% to 1.20% Mn, 0.50% to 1.40% Cr, 0.15% to 0.55% Mo, 0.0005% to 0.0050% B, 0.015% to 0.060% sol. Al, and proper amounts of Nb and/or Ti. According to the description of the technique described in patent literature 3, the steel contains a large amount of Cr and a large amount of Mo and hence, hardenability is enhanced and, at the same time, grain boundaries are strengthened thus enhancing low-temperature toughness.
Patent literature 4 proposes a method of manufacturing an abrasion resistant steel, wherein hot-rolling is applied to steel having the composition containing by mass %: 0.05% to 0.40% C, 0.1% to 2.0% Cr, proper amounts of Si, Mn, Ti, B, Al and N respectively and, further, Cu, Ni, Mo, and V as arbitrary components at a cumulative reduction ratio of 50% or more in an austenitic non-recrystallized temperature range at a temperature of 900° C. or below, thereafter, quenching is applied to a hot-rolled plate from a temperature of Ara transformation point or above and, subsequently, the quenched plate is tempered thus abrasion resistant steel being obtained. According to the description of this technique, directly quenching and tempering elongated austenite grains result the tempered martensitic structure where prior austenite grains are elongated. The tempered martensitic structure of the elongated grains remarkably enhances low-temperature toughness.
Further, patent literature 5 proposes an abrasion resistant steel plate having excellent low-temperature toughness and having the composition containing by mass %: 0.10% to 0.30% C, 0.05% to 1.0% Si, 0.1% to 2.0% Mn, 0.10% to 1.40% W, 0.0003% to 0.0020% B, 0.005% to 0.10% Ti and/or 0.035% to 0.1% Al. In the description of the technique described in patent literature 5, the abrasion resistant steel plate may further contain one or more kinds of elements selected from a group consisting of Cu, Ni, Cr and V. Due to such composition, in the technique described in patent literature 5, it is considered that the abrasion resistant steel plate has high surface hardness and exhibits excellent abrasion resistance and excellent low-temperature toughness.
Further, in patent literature 6, an abrasion resistant steel plate having excellent bending property is described. The abrasion resistant steel plate described in patent literature 6 is an abrasion resistant steel plate having the composition containing by mass %: 0.05% to 0.30% C, 0.1% to 1.2% Ti, and not more than 0.03% solute C, and having the structure wherein a matrix is formed of a ferrite phase and a hard phase is dispersed in the matrix. The abrasion resistant steel plate may further contain one or two kinds of components selected from a group consisting of Nb and V, one or two kinds of components selected from a group consisting of Mo and W, one or two kinds of components selected from a group consisting of Si, Mn and Cu, one or two kinds of components selected from a group consisting of Ni and B, and Cr. Due to such composition, in the technique described in patent literature 6, it is considered that both abrasion resistance and bending property against abrasion caused by earth and sand can be enhanced without inducing remarkable increase of hardness.